Service conditions for electronic components used in automobiles, industrial instruments etc. have changed remarkably, technical standards not yet required for those components conventionally have thus been amended accordingly, and applications thereof have been diversifying. As a result, electronic components for protecting electronic circuits vulnerable to unexpected noise or a large pulse are in high demand. Furthermore, it is in demand to take environmental influences of sulfuration, dew condensation etc. into account and to provide products with not only an initial function but also a continuously, highly reliable function.
Varistors functioning as a circuit protection device are divided into disk type (there are many devices of radial device type), surface mount type (chip type), and lamination layer (internal layer) device, and are properly used for respective applications. For example, the disk type is used for protection of 100V to 200V home appliances and peripheral circuits from high voltages and current pulses, such as a lightning surge. Moreover, the surface mount type and the lamination layer type are used for lower voltages and current pulses than those for the disk type. The higher the voltage and current type the larger the bulk size. This is because the smaller types cannot endure the lightning surge etc.
A chip varistor improved in surge current withstand for surge protection of electronic devices is disclosed in Patent Document 1, for example.